As is known in the art, a phased array antenna includes a plurality of antenna elements spaced apart from each other by known distances coupled through a plurality of phase shifter circuits to either or both of a transmitter or receiver. In some cases, the phase shifter circuits are considered part of the transmitter and/or receiver.
As is also known, phased array antenna systems are adapted to produce a beam of radio frequency energy (RF) and direct such beam along a selected direction by controlling the phase (via the phase shifter circuitry) of the RF energy passing between the transmitter or receiver and the array of antenna elements. In an electronically scanned phased array, the phase of the phase shifter circuits (and thus the beam direction) is set by sending a control signal or word to each of the phase shifter sections. The control word is typically a digital signal representative of a desired phase shift and may comprise a desired attenuation level and other control data.
Phased array antennas are often used in both defense and commercial electronic systems. For example, Active, Electronically Scanned Arrays (AESAs) are in demand for a wide range of defense and commercial electronic systems such as radar surveillance and track, terrestrial and satellite communications, mobile telephony, navigation, identification, and electronic counter measures. Military radar systems often require both long range operation for Ballistic Missile Defense (BMD) missions (requiring fully focused, high sensitivity beam patterns) and short range operation for volume surveillance missions (requiring spatially broadened beams to scan the surveillance volume faster). Such systems may also be used for electronic warfare (EW) and intelligence collection. Thus, the systems are often deployed on a single structure such as a ship, aircraft, missile system, missile platform, satellite, or a building.
When a phased array is deployed on a moveable platform (e.g., ship and airborne radar systems) it is often necessary to account for platform movement (e.g., ship pitch and roll) when pointing an antenna beam. Additionally, signal filtering or suppression to remove surface (horizon) clutter, electronic jamming, and other effects is typically necessary.
Many conventional phased array antennas accommodate movement by the use of agile beamforming and/or stabilized antenna mountings. However, such systems may be overly expensive or infeasible in the case of very large, high-powered phased arrays used for long-range surveillance. When the phased array antenna is mounted on the superstructure of a ship, for example, typical stabilization schemes are not possible. Often, existing algorithms employed to solve these problems employ an iterative “optimal search” scheme. In such applications, each antenna pattern variation or shaping for motion compensation requires independent real-time processing which becomes computationally intractable with narrow beam operation.
The combination of the long-range BMD and the short-range surveillance missions also poses a number of challenges to digital beamforming (DBF) in phased array systems. The typical high-power beam used for long-range searching is too narrow to effectively provide the large volume, rapid coverage needs of the short-range surveillance tasking. Although multiple simultaneous receive beams are typically formed to reduce occupancy time (and thereby improve volumetric coverage), such systems lack a sufficiently large transmit beam footprint to provide the necessary search coverage on time.
What is needed is an enhanced DBF approach capable of providing a flexible, broad beam transmit capability on a moving platform that can operate with multiple-beam simultaneous receive to provide clutter mitigation and pattern canting/shaping for motion compensation.